Stimulation of tissue in humans and other animals is used in a number of clinical applications as well as in clinical and general biological research. In particular, stimulation of neural tissue has been used in the treatment of various diseases including Parkinson's disease, depression, and intractable pain. The stimulation may be applied invasively, e.g., by performing surgery to remove a portion of the skull and implanting electrodes in a specific location within brain tissue, or non-invasively, e.g., transcranial direct current stimulation and transcranial magnetic stimulation.
A problem with tissue stimulation is an inability to monitor an effect of the stimulation on the tissue, particularly in real-time. For example, non-invasive stimulation of brain tissue involves stimulation of a large area of tissue that is generally not well characterized and that can be significantly perturbed by natural or pathological features of the brain tissue. The lack of monitoring makes it difficult to effectively target (localize) the stimulation to the desired region of tissue, dose the stimulation, and characterize safety parameters.